Loop antenna circuit



Patented Sept. 27, 1949 LOOP ANTENNA CIRCUIT Malcolm P. Herrick,Rochester, N. assigner t0. n y Stromberg-Carlson Company, a corporationof New York Application December 24, 1946, Serial No. 718,162

(Cl. Z50-40) Claims. l

This invention relates to antenna circuits for use in radio receiversand more particularly to means for coupling low impedance loop antennasto permeability tuned radio receiving systems.

Antenna circuits have been proposed heretofore in Which a permeabilitytuned inductance coil and a loop antenna have been connected in seriesbetween the input to the R. F. section of a radio receiving set andground, and the series combination is shunted by a variable capacitor.With this arrangement, the signal voltage induced in the loop is inseries with the antenna tank circuit. The loop antenna appears as aninductance in series with the tuning inductance. The ratio of maximum tominimum inductance of the coil is Li/Lz and the maximum to minimumfrequency ratio is (L2/L02. If the loop inductance L3, is considered,the inductance ratio becomes and the frequency ratio becomes Lad-133] L1+133 which is less than before. Because of the change in frequencyratio, the increased inductance renders diicult the obtaining ofsatisfactory tracking with other circuits.

An object of my invention is to provide a new and improved antennacircuit in which the effect of the antenna loop inductance is utilizedin a manner to improve tracking with other tuned circuits.

ther objects and advantages of my invention will be apparent from areading of the following description. The features of my invention whichI believe to be novel are set forth with particularity in the appendedclaims. My invention itself, both as to its organization and manner ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawing in which Fig. 1 is a schematicdiagram illustrating one form of my invention and Fig. 2 is a modicationof the circuit of Fig. 1.

Referring to Fig. 1, there is shown a suitable loop antenna l,preferably of low impedance, connected in series with a suitablevariable capacitor 3 between the input electrode element, such as thecontrol grid 6, of an elec-tron discharge device 4 Which may be part ofan R. F. amplifier, for example, and ground. A variable inductance coil2 is also connected between the input electrode or connection andground, i. e., in shunt with the loop I and capacitor 3. The coil 2 maybe tuned by a suitable ferromagnetic element 6 reciprocably arranged.The signal voltage induced in the loop I is in series with the tuningcapacitor 3 of the resonant antenna circuit and satisfactory trackingwith other circuits, such as the oscillator circuit, is readilyobtained. The cathode 1 of device 4 is connected to ground through aconventional bias resistor 8 shunted by a capacitor 9.

It has been found that if a resistor 5 of proper value is connectedacross the terminals of the loop when used with receivers of thesuperheterodyne type, as shown in Fig. 2, the image interference ratiois improved because any tendency of the loop and distributed circuitcapacitance to resonate in the image region of the system is damped out.Tracking is improved by thus shunting the reactance of the loop.

Because the circuits of Figs. 1 and 2 are essentially low impedancecircuits, some reduction in gain is obtained as compared withconventional circuits. This loss is more than made up, however, by theimprovement in tracking due to the shift of the stray capacitance.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from my invention in itsbroader aspects. I, therefore, aim in the appended claims to cover allsuch changes and modifications as fall Within the true spirit and scopeof my invention.

What I claim is:

1. In a radio receiver having an electron discharge device comprisinginput terminals, an antenna circuit comprising a capacitor, a loopantenna and an inductance coil, a ferromagnetic element reciprocablyarranged within said inductance coil for tuning said circuit over adesired frequency range, said antenna and said capacitor in series beingconnected across said input terminals and said coil being connected inparallel with said series-connected antenna and capacitor.

2. In a. radio receiver having an antenna circuit as dened in claim 1,resistance means shunting said loop antenna for damping out any tendencyof said loop and any distributed circuit capacitance to resonate in theimage region and for shunting the reactance of said loop antenna.

3. In a radio receiver having an antenna circuit as dened in claim 1,the loop antenna being of a low impedance type.

4. In a radio receiver, an input system com- 3 prising: a variableinduotance device adapted for tuning said input system over a range offrequenoies, said device having rst and second terminals; a seriesnetwork comprising a tuning capacitor and a loop antenna, connectedbetween said terminals; and a utilization circuit connected between saidterminals.

5. In Va radio receiver, an input system comprising: a variableinductancedevice'adaptedfor tuning said input system over a range offrequencies, said device having a high-potential terminal and alow-potential terminal; aseixies .net- Work comprising a tuningcapacitor and a `1oop antenna connected between 'said Iterminai's,

loop antenna being adjacent said low-potential terminal; and autilization circuit connected between said terminals.

MALCOLM P. HERRICK.

REFERENCES CITED The following references are of record in the ifile -of"this patent:

UNITED STATES PATENTS

